I don't believe live view on the Nikons work at least on the 2 NIkon's I've used: D5200 and D5300.
In the mean time I am assuming you want to do some focusing, what I do is use the frame and focus module. When I find the star that I want to use for focusing you can crop the view which will keep it's position. This is great so the next image you take you can watch the spikes or the stars get tighter. You can use click autostretch on the histogram so it brightens the image.
A bahnitov mask works best for this. If you do not have a mask you can click on the [star] icon at the top it will calculate the HFR value of the star and the smaller the value the better.
I use very short exposures / low ISO for this and it works quite well, 200 ISO with 2-3 seconds (Try different ones)
I do not use the JPG preview it does not provide a clean enough image than the regular raw one.
Hope that helps.